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Medicinal Herbs - What Defines Quality? |
 healing Orchid Sometimes people say to me that "Ive tried herbal medicine and it did nothing for me" and when i quiz them further on where they got there herbs and instructions on dose etc. its always pretty obvious why the herbs had no effect. Its very important when using herbal medicines to use good quality herbal preparations. So what defines Quality?
Medicinal herbs are sourced from nature
and hence, unlike conventional chemical
drugs, vary from batch to batch. This can
be readily understood by comparison with another
plant product — wine. In technical terms, wine is
the fermented juice of the fruit of Vitis vinifera.
However, factors such as the grape variety, climatic
conditions, soil type, time of harvest and fermentation
conditions can all determine whether a batch of
wine will be either poor or good quality (which is
subsequently reflected in the price of the wine).
In the case of wine, factors such as the texture,
colour, aroma and taste determine if the product is
of good quality or otherwise. For medicinal plants,
the situation is much more complex. Most of the
chemical components of herbs which are important
for therapeutic activity are secondary metabolites.
By definition, secondary metabolites are not
thought to be important for the growth and survival
of the plant, although they are sometimes produced
in higher levels in response to infection, insect
attack and adverse growing conditions. One consequence
of this is that even though they may give an
impression of quality, the appearance and colour of
a herb are not necessarily indicators of its therapeutic
quality. Indeed, plants grown under adverse
conditions may sometimes have a poor appearance
but higher levels of secondary metabolites. One
corollary of this is that while herb batches which
have a good appearance and a pleasant taste might
be suitable for a herbal tea, they may not be optimum
for use as medicines. An example is chamomile.
Chamazulene is considered to be an important
active component, and varieties of chamomile have
been bred which have higher levels of this compound.
Since chamazulene imparts a bitter taste to
the flowers, these high medicinal grade varieties are
not suitable for a herbal tea taken for pleasure.
How can the medicinal quality of a herb be determined?
One approach adopted by the various
pharmacopoeias and used by manufacturers is to
set minimum levels of marker chemical compounds
for a herbal raw material. These are seen to give an
indication of activity, and hence quality. This
approach is fraught with difficulties. Even where the
marker compound is known to contribute to the
therapeutic activity of the herb (and this is not
always the case), herbalists stress that the chemical
complexity of the plant confers the sum total of its
activity. But until we better understand how individual
herbs work in their chemical totality, it is a
good starting point.
The uncertainties can be
lessened by choosing phytochemical classes of
marker compounds (flavonoids, essential oil,
oligomeric procyanidins etc) rather than just
individual chemical components. In addition,
testing for different marker compounds (or groups
of marker compounds) in the one plant can lead to
a better assessment of activity. As one researcher
recently commented: “If a batch of a herb contains
low levels of one marker compound, and then by a
completely different test also shows low levels of
another class of marker compound, we can begin to
form the conclusion that it is of poor quality.”
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